Our recent work has involved studying relationships between heart period and blood pressure variability, using normal subjects and cardiac transplant recipients. In normals, we have demonstrated that the degree of resting heart period variability exerts antioscillatory effects on blood pressure variability responses to psychological and orthostatic challenge. In this current study, we wish to study these effects in patients with left ventricular assist devices (LVADs) set in both the fixed and variable modes. Subjects will be studied as inpatients in two sessions separated at most by one day. They will complete these sessions just prior to their discharge from the hospital. During the first session, the LVAD will be set in either the fixed or auto mode by random assignment. In the second session, the LVAD will be set in the other mode. On the morning of each session, subjects will be asked to hold their medications when the primary physician deems this to be permissable. To accomplish this, we will study 16 patients with LVADs. These patients will be studied in the supine and 40o upright (head-up) positions. While in the supine position, they will rest quietly for a 30 minute baseline. At the start of this baseline, the LVAD will be set either in the fixed mode at a rate of 15% higher that their normal sinus rate or in the auto mode, firing when the device is 80% full. Subjects then will respond to mental arithmetic and Stroop color-word matching tasks, each for 5 min. After these psychological tasks and a 15 min recovery period, they will be tilted upright for 10 min. During the entire protocol, subjects will be monitored for ECG, noninvasive beat-to-beat blood pressure, and respiration. In addition, data from their LVAD will be recorded.